Cover Up! The absolute best and least harmful way to repel insects is to stay covered (with light colored clothing). You can also spray your clothes with bug spray and still avoid some of the risks associated with putting chemicals on your skin. In hot and humid environments, wearing clothes can be incredibly uncomfortable and bug repellents are the only option. There are a variety of different solutions you can use to make yourself less attractive to insects such as mosquitos, ticks, horseflies, and noseeums.
This is still considered to be the most effective bug repellent, although many people believe that it is harmful to people. Of course DEET manufacturers adamantly deny these accusations, and scientific studies come up with opposing answers. Levels of DEET vary in different products, up to almost 100% DEET. If you are traveling or backpacking in an area where mosquitos are aggressive and carry malaria, yellow fever, West Nile Virus, or other pathogens, or where there are ticks, the negative side effects of getting a disease probably outweigh the downsides of using a chemical-based repellent such as DEET. The best combination is to wear both DEET and loose fitting, light-colored clothing.
If you are backpacking in an area where the repercussions of an insect bite are just irritating bumps, you may want to try a more natural solution. Most of them are not scientifically proven to work consistently, however testimonials show time and time again that they can help reduce insect nuisances. A few chemical-free options are lemongrass-eucalyptus spray, citronella candles, peppermint oil, cedar, lemongrass, and castor oil. Dietary changes such as eating garlic and taking vitamin B pills are not proven to make any difference. Some sunscreens contain bug repellant, however many health experts warn against this 2-in-1 because sunscreen needs to be applied often and generously, whereas insect repellent, especially the ones containing DEET, should be applied sparsely and as infrequently as possible.